WHEN WILL THERE BE AN AVERAGE SEX DIFFERENCE IN A PARTICULAR TRAIT

WHEN WILL THERE BE AN AVERAGE SEX DIFFERENCE IN A PARTICULAR TRAIT?

To answer this question, we need to know two things:

1. We need to know if the trait results from an adaptation that is sexually monomorphic or sexually dimorphic.

2. We also need to know if the “sex role” socialization of a particular culture is monomorphic (males and females socialized the same with respect to the trait), dimorphic to maximize the sex difference, or dimorphic to minimize the sex difference.

	EVOLVED ADAPTATION IS SEXUALLY:
“SEX ROLE” SOCIALIZATION:	MONOMORPHIC	DIMORPHIC
Monomorphic	No sex difference	Sex Difference
Dimorphic – socialization that tends to increase a sex difference	Slight sex difference	Sex Difference -- possibly large
Dimorphic – socialization that tends to reduce a sex difference	Slight sex difference	Variable – depending on the degree of the dimorphism of adaptation

EXAMPLE: Height (a strongly sexually dimorphic adaptation)

	ADAPTATION IS SEXUALLY:
“Sex Role” Socialization:	Monomorphic	Dimorphic
Monomorphic		Sex Difference – avg 2 Std Deviations
Dimorphic – socialization that tends to increase a sex difference		Sex Difference -- possibly larger than typical
Dimorphic – socialization that tends to reduce a sex difference		Sex Difference -- possibly smaller than typical

EXAMPLE: Head hair length (a sexually monomorphic adaptation)

	ADAPTATION IS SEXUALLY:
“Sex Role” Socialization:	Monomorphic	Dimorphic
Monomorphic	No sex difference
Dimorphic – socialization that tends to increase a sex difference	Sex difference in hair length
Dimorphic – socialization that tends to reduce a sex difference	No sex difference in hair length

If a sex difference is based on a monomorphic adaptation, then the magnitude of sex difference will vary across cultures, and it will vary in both directions, depending on sex role socialization. One can expect to see many sex difference “reversals” across cultures, perhaps with close to 50% of the cultures “reversed” on the sex difference.

If a sex difference is based on a dimorphic adaptation, then the magnitude of the sex difference will vary somewhat across cultures. However, the direction of the sex difference will tend to remain (e.g., males > females, or vice versa), and very few cultures will be found in which the sex difference is reversed.

It is very likely that “sex drive” is a sexually dimorphic adaptation, both for theoretical, evolutionary reasons, as well as the fact is that we see few, if any, sex difference reversals for this trait across time and cultures.

EXAMPLES: Hair length (sexually monomorphic) and sex drive (sexually dimorphic)

	ADAPTATION IS SEXUALLY:
“Sex Role” Socialization:	Monomorphic HAIR LENGTH	Dimorphic SEX DRIVE
Monomorphic	No sex difference	Sex Difference, M > F
Dimorphic – socialization that tends to increase a sex difference	Sex difference in hair length	Large Sex Difference, M > F
Dimorphic – socialization that tends to reduce a sex difference	No sex difference in hair length	Smaller Sex Difference, M > F, or no sex difference (M = F)

MONOMORPHIC

DIMORPHIC

Monomorphic

It is very likely that “sex drive” is a sexually dimorphic adaptation, both for theoretical, evolutionary reasons, as well as the fact is that we see few, if any, sex difference reversals for this trait across time and cultures.